In the field typically of transportation equipment and construction equipment, single-layer or multilayer welding in a fillet or groove is often performed through gas metal arc welding. This technique employs a high welding current to perform welding at a higher wire melting speed so as to achieve a higher efficiency. However, such an increased current density causes generation of spatters in large amounts, and this causes inferior appearance of the weld beads and requires an extra step for removing the spatters, resulting in an insufficient production efficiency.
Solid wires are generally used in the field. However, when used in welding at a high current density of 300 A/mm2 or more, the solid wires present a droplet transfer mode called rotating transfer. Specifically with reference to FIG. 2A, excessive Joule heating in a wire extending portion 1 ranging from a contact tip to an arc generation spot causes the wire to be softened and melted to thereby elongate from its tip, and the resulting tip molten metal 2 transfers while rotating with an arc 4.
In addition to the rotating transfer, exemplary droplet transfer modes further include globular transfer as illustrated in FIG. 2B in which a molten droplet 3 having a size larger than the outer diameter of the wire extending portion 1 transfers while being repelled; and spray transfer as illustrated in FIG. 2C in which a molten droplet 3 having a size smaller than the outer diameter of the wire extending portion 1 transfers. In the rotating transfer, most of the pinched-off molten droplet spatters to surroundings, thus causing a remarkable spatter generation rate. In the globular transfer, a large amount of large-sized spatters is generated. In the spray transfer, a small amount of spatters is generated. Accordingly stabilization of spray transfer is a key to reduce spatter generation rate.
Independently, the following welding methods have been proposed in known techniques as methods for performing gas-shielded arc welding at high current densities typically in fillet welding and multilayer welding.
JP-A No. S59 (1984)-45084 proposes a welding method to attain a high deposition rate (amount of deposited metal) by using a solid wire as an electrode wire and using a four-component gaseous mixture containing 40 to 70 percent by volume of argon, 25 to 60 percent by volume of helium, 3 to 10 percent by volume of carbon dioxide, and 0.1 to 1 percent by volume of oxygen as a shielding gas.
JP-A No. H03 (1991)-169485 proposes a welding method to attain a high deposition rate and to attain a bead smoothing effect by the action of slag, in which welding is performed with a slag-based flux-cored wire as an electrode wire and carbon dioxide gas as a shielding gas at a current density of 300 A/mm2 or more.
JP-A No. H03 (1991)-35881 proposes a welding method to attain a good penetration shape, in which welding is performed using a solid wire and a shielding gas at a current density of 300 A/mm2 or more, where the solid wire has a resistivity ρ of 25 to 65 μΩ·cm and contains sulfur (S) in a content of 0.010 to 0.040 percent by mass, and the sulfur content and the resistivity ρ satisfy the condition: K=20 to 40 wherein K=505·S+0.41·ρ; and the shielding gas is a gaseous mixture containing CO2 in a content of 2 to 20 percent by volume and O2 in a content of 1 to 10 percent by volume with the remainder being argon (Ar), in which the CO2 content and the O2 content satisfy the condition: [CO2+2×O2]≥20 percent by volume.